Got it. "There isnt really anything that its doing" is going to throw anyone off. You wouldn't be needing help if nothing was wrong. :)
Two things come to mind. First of all, GM had a huge problem with the electrical ground on the fuel tank when they get rusty. Intermittent no-start was the most common complaint but they could also cause stalling while driving. A fix that was much more reliable than the original design was to drill a small hole in the tank's flange outside of the seam weld, and use a self-tapping screw to attach a ground wire. The other end of the wire was attached to the frame or body sheet metal. That only applies to the steel fuel tanks. Newer models use a plastic tank. Don't go drilling any holes in that one! Those already have a separate ground wire. Banging on the metal tank can disturb the two metal straps and cause them to make enough of a connection to get the pump to run. If this is the problem, you will find that the pumps that are removed will run just fine when connected to a battery with jumper wires.
The other thought has to do with repeat pump failures on Chrysler products but it might apply to your vehicle too. Chrysler fuel pumps are extremely quiet compared to other brands of vehicles but it comes at a price. They are built to very close tolerances to make them quiet but the impellers can become clogged from a buildup of microscopic debris in the tank. The typical scenario is you buy a replacement pump from the auto parts store, and it fails within a few weeks. They replace it under warranty and the new one fails in a few weeks. You try a couple of pumps from a different store and the same thing happens. Out of desperation, you buy the entire pump assembly from the dealer and have no more problems. The assumption is the aftermarket pumps are junk. In reality, those pumps are fine, in fact, NAPA is one store I'm aware of that buys their replacement Chrysler pumps from the same supplier that builds the original ones for Chrysler.
What is really happening is that microscopic junk in the tank is getting stuck in the new pumps. By the fourth or fifth pump, all of that stuff has been removed so the next one doesn't get plugged. That next one happens to be from the dealer. What more and more people are finding out is to prevent repeat failures, they are having the tanks steam cleaned by radiator repair shops before installing the new pumps. I don't know where that debris comes from but this is a common enough problem that it is becoming well known.
There are other things that can cause the pump to not run, but your dandy observation, (thank you), that banging on the tank got the pump going really narrows down the list of suspects. If you have a metal tank, the next time the pump doesn't run, use a grounded test light and touch the probe right on the tank. If the test light lights up, the tank has a bad ground. With a bad ground, the pump can't run.
Wednesday, October 6th, 2010 AT 1:04 PM